Power steering pump

ABSTRACT

A power steering pump having a cam with an internal cam surface defining pumping arcs, a rotor in said cam, pumping elements preferably in the form of slippers carried by the periphery of the rotor in sliding engagement with the pumping arcs, flow control valve means having a movable valve element responsive to both static pressure and velocity pressure of the displaced fluid on the high pressure side of the pump wherein provision is made for decreasing the volume of fluid delivered by the pump at high pressure upon an increase in the speed of the rotor, and means for equalizing the pressure between the volume of fluid between two adjacent pumping elements located at a high pressure outlet port and a corresponding volume of fluid between two other adjacent slippers located at a low pressure inlet port as the pumping elements pass through their respective pump cycles.

BRIEF DESCRIPTION OF THE INVENTION

My invention relates to improvements in power steering pumps such asslipper pumps of the kind disclosed in U.S. Pat. Nos. 3,614,266 and3,645,647 as well as in pending patent application Ser. No. 885,912,filed Mar. 13, 1978, said patents and said application being assigned tothe assignee of this invention.

The pump of my invention comprises a cam that surrounds a rotor. The camhas two pumping arcs situated 180° out of position with respect to eachother. The rotor carries multiple pumping elements or slippers whichengage the cam surface surrounding the rotor. End plates are situated oneither side of the cam and rotor, and these plates are provided withports which admit fluid to each of the two pumping chambers defined bythe cam and the rotor.

The fluid is displaced by the pumping elements or slippers as theytraverse the pumping arc from the inlet port to the outlet port. Afteradjacent pairs of pumping elements traverse the outlet high pressureport, the volume of fluid in the cavity located between those twoslippers is pressurized at the pressure value of the outlet pressure.Normally in a pump of this kind the volume of fluid trapped between thetwo adjacent slippers is exhausted to the inlet port as the pumpingelements further progress upon rotation of the rotor.

At the instant that two adjacent pumping elements traverse the outletport, two other adjacent pumping elements are traversing the inlet port.They too define a volume of fluid therebetween that is equal in pressureto the inlet pressure of the pump. Upon further rotation of those twoadjacent slippers, the low pressure fluid in the trapped volume betweenthem is brought into communication with the outlet port. Thus there aretwo rapid changes in pressure of trapped volumes of fluid betweenadjacent slippers during each pumping cycle. There are two pumpingcycles for each revolution of the rotor. This condition establishespressure pulsations which may cause pump noise and which reduce pumpingefficiency.

According to a feature of my invention I have made provision forequalizing the pressures between the two trapped volumes of fluid sothat the trapped volume of fluid adjacent the pump outlet port isreduced and the trapped volume fluid adjacent the inlet port isincreased. This is done by providing suitable pressure equalizationchannels in either or both of the pressure plates located adjacent therotor in the cam. Some of the potential energy of the pressurized volumeof fluid trapped between two adjacent pumping elements near the outletport is recovered as the high pressure in that trapped volume isdistributed to the low pressure volume trapped between two adjacentpumping elements near the inlet port.

According to another feature of my invention I have provided a flowcontrol valve for controlling the pressure and flow whereby the pressureof the fluid displaced by the pump increases at a relatively fast rateupon an increase in rotor speed during low and intermediate speedoperation and wherein the rate of fluid delivery by the pump at highspeeds is relatively constant upon a further increase in the rotorspeed. This reduces the effective horsepower required to drive the pumpat high speeds and avoids excessive fluid delivery in pump applicationssuch as vehicle power steering systems for automotive vehicles where therotor is connected drivably to the vehicle engine and the pump normallytends to deliver an excessive amount of fluid to accomplish steeringfunctions during high speed operation.

Another feature of my invention is a strategic porting of the flowcontrol valve described in the foregoing paragraphs which causes asupercharger effect as fluid is returned to the pump circuit from thereservoir for the pump to the flow control valve. The direction of theflow from the reservoir to the flow control valve is such that thevelocity pressure developed by the flow augments the pressure at thepump inlet port.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a pump embodying the improvements ofmy invention.

FIG. 2 is a cross-sectional view taken along section line 2--2 of FIG.3.

FIG. 3 is a side elevation view of the pump of FIG. 1.

FIG. 4 is an end view of the pump of FIG. 1 as seen from the plane ofsection line 4--4 of FIG. 3.

FIG. 5 is a cross-sectional view of the end plate as seen from the planeof section line 5--5 of FIG. 1.

FIG. 6 is a cross-sectional view of the pump end plate seen in FIG. 1.

FIG. 7 is an end view of the end plate of FIG. 6 as seen from the planeof section line 7--7 of FIG. 6.

FIG. 8 is a cross-sectional view of the other end plate in the assemblyof FIG. 1.

FIG. 9 is an end view of the end plate of FIG. 8 as seen from the planeof Section line 9--9 of FIG. 8.

FIG. 10 is a subassembly view of the rotor and cam of the assembly ofFIG. 1 as seen from the plane of section line 10--10 of FIG. 1.

FIGS. 11A and 11B are schematic cross-sectional views of the valveassembly shown in FIG. 2 with the movable spool portion of the valveassembly in the low-speed condition and the high-speed condition,respectively.

FIG. 12 is a schematic representation of a rotor and cam assembly of thetype shown in FIG. 10. The view of FIG. 12 is a schematiccross-sectional view taken on spaced, parallel cross-sectional planes toshow the equalizer passages of either side of the rotor.

PARTICULAR DESCRIPTION OF THE INVENTION

In FIG. 1 numeral 10 designates a pump housing which may be formed ofcast aluminum or other suitable material. It is provided with a pumpcavity 12, the left hand end of which is closed by housing wall 14. Theright hand end of the cavity 12 is closed by end cover 16 which is inthe form of a plate received in the opening 12 and held in place by asnap ring 18. A fluid reservoir 20 formed of fiberglass or some othersuitable material is situated with its margin surrounding the margin 22of the housing 10. It encloses the end cover plate 16, the latterforming a valve housing for the valve assembly indicated generally byreference numeral 24.

The interior of the reservoir 20 communicates with return flow passage26, which communicates with the low pressure side of a fluid pressureoperated mechanism such as a power steering gear for an automobile.

A pump cam 28 is situated in the housing opening 12. As best seen inFIG. 10, cam 28 defines a pair of pumping arcs 30 and 32 which arejoined together by two sealing arcs 34 and 36 to define a continuous camsurface of irregular shape. The periphery of the rotor 38 is providedwith multiple recesses 40 each of which receives a fluid pumping elementsuch as slipper 42. In the embodiment disclosed each recess is providedwith a radial opening that receives a spring 44 which urges theassociated pumping element or slipper radially outward into cammingengagement with the internal cam surface.

A lower pressure plate 46 is situated on the left hand side of the rotor38 as seen in FIG. 1, and an upper pressure plate 48 is located on theright hand side of the rotor 48. End plate 16, which forms the valvebody for the flow control and pressure relief valve assembly 24, isreceived within the opening 12 in the pump housing and is situateddirectly adjacent the upper pressure plate 48. The lower pressure plate46, the rotor 38, the upper pressure plate 48 and the end plate 16 areheld in axially stacked relationship and are urged into sealingengagement, one with respect to the other, by fluid pressure in theinner pressure chamber 50 at the base of the opening 12. Snap ring 18provides the force reaction for the pressure force developed by thepressure in the pressure chamber 50. One or more pilot pins 52 receivedthrough the cam 28 and the two pressure plates as well as the end plateto hold the assembly in proper angular registry.

The lower pressure plate 46 is seen in the detailed views of FIGS. 6 and7. The right hand surface of the pressure plate 48 is seen in FIG. 6 at52. It is formed with low pressure ports 54 and 56 and with highpressure ports 58 and 60. Low pressure ports 54 and 56 communicaterespectively with low pressure ports 62 and 64 in the cam 28. The lowpressure ports communicate with the inlet portion of the pumping chamberdefined by the cam ring and the pump rotor. The spaces located betweentwo adjacent pumping elements or slippers communicate with the inletports as they move through the pumping arc and expand in volume. Thespaces between the same two adjacent pumping elements or slippers, asthey decrease in volume upon continued rotation of the rotor through thepumping cycle, communicate with high pressure ports 58 and 60. Theycommunicate also with high pressure ports 66 and 68 located in upperpressure plate 48. The inlet ports in the upper pressure plate 48corresponding to the inlet ports 54 and 56, respectively, in the lowerpressure plate 46, are shown at 70 and 72.

The high pressure ports communicate with pump outlet passage 74 as seenin FIG. 2 and the low pressure ports communicate with low pressurereturn passage 76, also seen in FIG. 2. These passages are located inthe end plate 16 which contains the valve assembly 24. This can best beseen by referring to FIG. 5 which shows the passages in the face of theend plate 16 that engages the upper pressure plate 48.

The cam ring 28, which is received within the opening 12 of the housing,defines with the housing a low pressure chamber 78. That space is influid communication with the seal chamber 80 seen in FIG. 1, suitableinternal porting 81, as shown in FIG. 4, being formed in the housing 10for that purpose.

Drive shaft 82 for the rotor 38 extends through an opening 84 formed inthe housing 10 and is journalled in that opening by a suitable bushingas shown. Shaft 82 is splined at 86 to an internally splined openingformed in the rotor 38.

The high pressure passage 74 is in communication with venturi throat 88formed in the venturi flow control element 90. That element is threadedat 92 within a threaded portion of the valve opening 94. The other endof the venturi passage 88 communicates with outlet passage 96 formed ina venturi element 90.

Element 90 is provided with a shoulder 98 which registers with anopening formed in the reservoir 20 to hold the reservoir fast againstthe end plate 16. That connection and the registry of the margin of thereservoir 20 with the outer periphery of the housing 10 providesstability for the reservoir. The margin of the reservoir 20 is providedwith an O ring or other seal 100.

Venturi pressure passage 102 is formed in the venturi element 90, and itis in communication with the throat 88. Internal passages formed in theend plate 16 connect the passage 102 with the right hand end 104 of thevalve opening 94. Valve spool 106, having spaced valve lands 108 and110, is slidably positioned in the valve opening 94. Valve spring 113 issituated at the end 104 of the opening 94 and urges the valve element106 in a left hand direction as seen in FIG. 2. The outlet pressure inpassage 74 tends to urge the valve element 106 in a left hand directionagainst the opposing force of the spring 113. As it does this, land 108uncovers port 76 thereby bypassing the pumped fluid to the low pressureside of the pump. The fluid that is not bypassed is distributed throughthe venturi throat 88 to the outlet passage 96. As the pump speedincreases, the flow through the venturi throat increases, therebyestablishing a reduced venturi pressure which is transmitted to the end104 thereby causing a reduced pressure at that point that causes thespool valve to move to a more fully opened position thereby bypassingmore fluid and reducing the effective outlet flow. Conversely, adecrease in pump speed will result in a build-up in pressure in the end104 thereby augmenting the spring force and causing a decreased bypassflow.

A pressure relief valve 112 registers with a relief orifice 114 in thevalve element 106. It is normally closed by valve spring 116. Upon anexcessive pressure buildup the pressure transmitted to the right handside of the valve opening will cause the valve 112 to become unseatedthereby bypassing fluid to the inlet side of the pump and relieving theexcessive pressure.

FIGS. 11A and 11B show in generally schematic fashion the valvestructure of FIG. 2 and reference will be made to it to explain theoperation of the valve. FIG. 11A shows a low-speed, high-pressurecondition of the valve, and FIG. 11B shows the high speed conditionwhere part of the outlet flow of the pump is bypassed.

In the valve of FIGS. 11B and 11B fluid is bypassed from the pump outletpressure passage 74 to low pressure port 76 when the valve land 108uncovers the port 76. Any fluid not bypassed through port 76 will betransmitted to the outlet passage 96, thereby creating a venturipressure which is distributed to internal passage 118 from the throat102 to the opposite side of the valve element 106. After the pump speedincreases above a predetermined value, a second control port 120 becomesuncovered by land 110. This port 120 communicates with the passage 118.When the port 120 is uncovered, the low pressure area that communicateswith port 122 is brought into communication with passage 118. Port 122,in turn, communicates with the reservoir and fluid is returned from thereservoir to the valve assembly through it. As soon as passage 118becomes subjected to lower pressure, valve element 106 will be caused toshift further away from the venturi throat thereby increasing the bypassflow from port 74 to port 76 and decreasing the outlet flow through thepassage 96. Thus a decrease in the rate of pressure build up uponincrease in pump speed occurs and this causes a so-called "drooper"effect. A drooper effect is achieved in other ways in other prior artconstructions, such as those shown in U.S. Pat. Nos. 3,253,607 and3,349,714. The drooper effect in the '607 patent is achieved by using apair of flow metering orifices and controlling the effectiveness of oneof the orifices as flow across the mouth of the orifice increases. Thedrooper effect of the '714 patent is achieved by having a variablegeometry metering pin register with an orifice in the outlet flowcircuit of the pump. The drooper effect of my instant invention isachieved in a much simpler fashion, and it is characterized by improvedreliability.

FIG. 11B shows the valve element 106 in a position where the 1 and 110uncovers the port 120, which corresponds to the high speed condition.

Upper pressure plate 48 as well as the lower pressure plate 46 isprovided with pressure equalizer passages. Each pressure plate has apair of passages, one corresponding to each of the pumping chambers ofthe pump. Equalizer passages for the upper pressure plate 48 are shownat 124 and 126, which span the inlet ports 70 and 72 respectively. Theyare arcuate in form, and their ends are located close to the cutoff andopening edges of the ports to which they are adjacent. The equalizerpressure passages for the lower pressure plate 46 are shown at 128 and130. As in the case of the equalizer pressure passages for the upperpressure plate, passages 128 and 130 span the inlet ports 54 and 56; andthey terminate a location adjacent the individual edges of these ports.

In order to explain the operation of the equalizer pressure passages,reference will be made to FIG. 12 where I have shown in schematicfashion a cam and rotor assembly. I have identified the equalizerpressure passages by reference characters 128' and 130' which correspondto the passages 128 and 130 of FIG 7. The direction of rotor rotation isillustrated by the rotational vector 132. The two low pressure oil inletports are identified in the schematic sketch of FIG. 12 by referencecharacters 134 and 136. The two outlet high pressure ports areidentified in the schematic sketch of FIG. 12 by reference numerals 138and 140. The rotor 142, which corresponds to the rotor 38 in theembodiment of FIGS. 1 through 9, carries slippers 144 located in radialpockets 146. The equalizer pressure passage 128' of the rotor 142 ispositioned as shown in FIG. 12 establishing communication between thepockets located at the 1:30 o'clock position and the 10:00 o'clockposition. The fluid cavity located between two adjacent slippers at the11:30 o'clock and the 1:30 o'clock positions becomes trapped after thesecond of the pair of slippers passes the cutoff edge 148 of the highpressure outlet port 138. At the same instant the slipper at the 10:00o'clock position has just passed the cutoff edge 150 of the oil inletport 134. Thus the fluid trapped in the cavity between the slippers atthe 10:00 o'clock position and the 8:30 o'clock position is equal inpressure to the pressure at the inlet port 134. Conversely, the pressurethat exists in the trapped volume of fluid between the slippers at the11:30 o'clock position and the 1:30 o'clock position is at the highpressure that exists in the outlet port 138.

It should be noted that the leading edge of each slipper pocket 146 isprovided with an angular slot 147 which permits the pocket 146 tocommunicate with the pumping chamber between that slipper and the nextadjacent preceding slipper. Corresponding notches are shown also in FIG.10 at 41.

The pressure equalizer passage 128' will cause a higher pressure to bedistributed to the trapped volume of fluid at the lower pressure,thereby tending to equalize the pressures and permitting a recovery ofsome of the potential energy of the fluid. When the trapped volume ofhigh pressure reaches the oil inlet port 134 upon continued rotation ofthe rotor, the pressure change that occurs is less severe and pressurepulsations tend to be modified or reduced. The same is true for thetrapped volume of fluid at the lower pressure port as it is brought intocommunication with the high pressure outlet port 140 upon continuedrotation of the rotor. The pressure difference between that trappedvolume of fluid and the pressure at the outlet port 140 is reduced. Thispressure equalization improves the pumping efficiency and reduces pumpnoise due to large pressure pulsations.

Equalizer pressure passage 130' functions in a similar fashion on theopposite side of the pump as fluid is transferred from the inlet port136 and to the outlet port 138.

Having thus described a preferred embodiment of my invention, what Iclaim and desire to secure by U.S. Letters Patent is:
 1. A positivedisplacement pump comprising a pump rotor and a cam ring surroundingsaid rotor and having a noncircular inner surface, said rotor and saidcam ring defining therebetween crescent shaped pumping cavities, endplates situated on either side of said rotor and said cam ring, said endplates, said cam ring and said rotor being disposed within a pumphousing, a plurality of recesses formed in the periphery of said rotor,a pumping element registering with each recess and disposed in slidingengagement with said cam ring, fluid inlet ports and fluid outlet portscommunicating with said pumping cavities in arcuately displacedlocations one with respect to the other, each pair of pumping elementsand the cooperating end plates and cam ring defining a fluid cavity, afirst fluid cavity defined by a first pair of said pumping elements anda second fluid cavity defined by a second pair of said pumping elementsbeing disposed at a first angular position of said rotor adjacent aninlet port and an outlet port, respectively, and equalizer pressurepassage means formed in said end plates, said equalizer pressure passagemeans being angularly situated with respect to said ports to establishfluid communication between said first pressure cavity and said secondpressure cavity at the angular rotor position at which said firstpressure cavity begins to communicate with an outlet port and saidsecond pressure cavity begins to communicate with an inlet port wherebythe higher pressure in said second cavity is reduced as the first cavityis prepressurized.
 2. A positive displacement pump comprising a pumprotor and a pump cam surrounding said rotor, said cam being out-of-roundand its internal surface cooperating with said rotor to define twocrescent shaped pumping chambers situated 180° out of phase with respectto each other, members defining a wall on either side of said rotor andcooperating with said rotor and said cam to define said pumpingchambers, a separate inlet port and a separate pump outlet portcommunicating with each crescent pumping chamber, a plurality ofrecesses formed in the periphery of said rotor, a pumping elementsituated in each recess and arranged in sliding engagement with theinternal surface of said cam, each adjacent pair of pumping elementscooperating with said cam, said rotor and said walls to define apressure cavity, the pressure cavity defined by a first of said pairs ofpumping elements communicating with the pumping cavity defined by asecond of said pair of pumping elements during rotation of said rotor atthe rotor position where said first cavity is moved out of registry witha first high pressure port and the pressure cavity associated with saidsecond pair of pumping elements is moved out of registry with respect toa first low pressure inlet port, an equalizer pressure passage meansestablishing such communication.
 3. The combination as set forth inclaim 2 wherein the fluid in the pressure cavity defined by a thirdadjacent pair of said pumping elements communicates with the pressurecavity defined by a fourth adjacent pair of said pumping elements whenthe former pumping chamber moves out of registry with respect to anotherhigh pressure port and the pressure cavity defined by the said fourthpair of said pumping elements moves out of registry with another inletport, said communication being established by second equalizer pressurepassage means.